Short answers, pulled from the story.
The Daugava rises in the Valdai Hills of Russia, close to the source of the Volga, and flows westward through Belarus and Latvia before emptying into the Gulf of Riga of the Baltic Sea. Its total length is 1,020 kilometres, with 352 kilometres in Latvia and 325 kilometres in Russia.
According to Max Vasmer's Etymological Dictionary, the name Dvina likely derives from an Indo-European word meaning 'river' or 'stream', related to the Proto-Indo-European root danu, meaning 'large river'. The Finno-Ugric name for the river comes from the Proto-Finnic word vain, roughly meaning 'a large, peacefully rolling river'.
Beginning around the sixth century CE, Viking explorers used the Daugava as a route into the Baltic interior. In medieval times, the river was part of the trade route from the Varangians to the Greeks, carrying furs from the north and Byzantine silver from the south.
The Kegums Hydroelectric Power Station was built between 1936 and 1939. The Plavinas Hydroelectric Power Station entered operation in 1968 and the Riga Hydroelectric Power Plant in 1974.
In Belarus, water pollution of the Daugava is considered moderately severe, with chief sources being treated wastewater, fish-farming, and agricultural chemical runoff including herbicides, pesticides, nitrates, and phosphates. Environmental deterioration began in the Soviet era, driven by collective agriculture and hydroelectric power projects.
High nitrate and phosphate loads from the Daugava have contributed to extensive phytoplankton buildup in the Baltic Sea. The Daugava's catchment area of 87,900 square kilometres, largely in Belarus, means agricultural runoff accumulates along its full length before reaching the sea.